The invention relates to an electrodeless low-pressure discharge lamp provided with a light-transmitting discharge vessel which encloses a discharge space in a gastight manner and which is made of a glass comprising at least 5% by weight of sodium oxide and has a filling comprising mercury, which lamp is in addition provided with means for maintaining an electric discharge in the discharge space.
An electrodeless low-pressure discharge lamp, also referred to in the present description and claims as "lamp", is understood to be a low-pressure discharge lamp in which the discharge is maintained by means other than electrodes situated inside the discharge vessel. The means for maintaining the discharge may comprise, for example, a microwave generator. Electrodes may be present for different purposes. For example, one or several, for example external electrodes may be present for promoting lamp ignition. Lamps of the kind described in the opening paragraph may have a comparatively long life owing to the absence of electrodes which are permanently loaded during nominal operation compared with lamps which do have electrodes.
An electrodeless low-pressure discharge lamp of the kind described in the opening paragraph is known from EP 0 162 504. The discharge vessel of the known lamp is made partly from lime glass and partly from lead glass. These glasses are easy to process and have the advantage that they substantially do not transmit UV-C radiation (&lt;280 nm) which is detrimental to human health. Mercury resonance radiation generated in the discharge space of the lamp cannot reach the surroundings of the lamp as a result. In the known lamp, the means for maintaining the discharge comprise a first and a second winding of an electric conductor around a core of magnetic material. To ignite the known lamp, an ignition voltage is applied across the first winding, which voltage is comparatively high compared with the voltages across this winding during nominal operation. The supply device is comparatively heavily loaded during this.
The known lamp has the disadvantage that the ignition time, i.e. the time interval between the moment at which an ignition voltage is offered and the moment when a discharge comes into being, is comparatively long, especially when the lamp has been out of action for a few days. As a result, special measures are necessary for avoiding the life of the supply device from being adversely affected.